low
3.5
CWE
200 863
Advisory Published
Advisory Published
Updated

CVE-2021-39164: Improper authorisation of /members discloses room membership to non-members

First published: Tue Aug 31 2021(Updated: )

### Impact Unauthorised users can access the membership (list of members, with their display names) of a room if they know the ID of the room. The vulnerability is limited to rooms with `shared` history visibility. Furthermore, the unauthorised user must be using an account on a vulnerable homeserver that is in the room. ### Patches Server administrators should upgrade to 1.41.1 or later. ### Workarounds Administrators of servers that use a reverse proxy could, with potentially unacceptable loss of functionality, block the following endpoints: * `/_matrix/client/r0/rooms/{room_id}/members` with `at` query parameter * `/_matrix/client/unstable/rooms/{room_id}/members` with `at` query parameter ### References n/a ### For more information If you have any questions or comments about this advisory, e-mail us at security@matrix.org.

Credit: security-advisories@github.com security-advisories@github.com

Affected SoftwareAffected VersionHow to fix
Matrix Synapse<1.41.1
Fedoraproject Fedora=34
Fedoraproject Fedora=35
pip/matrix-synapse<1.41.1
1.41.1

Remedy

https://github.com/matrix-org/synapse/commit/cb35df940a

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Reference Links

Frequently Asked Questions

  • What is CVE-2021-39164?

    CVE-2021-39164 is a vulnerability in Matrix Synapse versions 1.41.0 and prior that allows unauthorized users to access the membership (list of members) of a room if they know the room ID and the room has shared history enabled.

  • What is the severity of CVE-2021-39164?

    The severity of CVE-2021-39164 is low, with a CVSS severity score of 3.1.

  • How can unauthorized users access the membership of a vulnerable room in Matrix Synapse?

    Unauthorized users can access the membership of a vulnerable room in Matrix Synapse if they know the room ID and the room has shared history enabled.

  • Which versions of Matrix Synapse are affected by CVE-2021-39164?

    Matrix Synapse versions 1.41.0 and prior are affected by CVE-2021-39164.

  • How can I fix CVE-2021-39164 in Matrix Synapse?

    To fix CVE-2021-39164, upgrade to version 1.41.1 or later of Matrix Synapse.

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